Dear Tim, 

If you are almost positive you have a vocation to the priesthood and your parents agree, it would be good to look into a high school seminary if your diocese has one or if you know of one. 

If this is not possible, keep up your prayer life, keep up your studies, take part in sports, do some service or missionary activity with an apostolic group (if you don't know of one write back to me and tell me where you are from and I will try to connect you up with one). Over the next few years visit the seminaries you are interested in, and I think you will find that things will become clearer when it comes closer to the time to take a step. 

God bless.